Clinical examination and treatment of retinal disease has not fundamentally changed in the last 100 years, relying on a slit lamp biomicroscope which consists of a binocular stereo microscope, a handheld condensing lens, and a slit lamp providing illumination to examine the retina, as seen in FIG. 1A. A slit beam of light is created by the slit lamp and shone through a handheld lens placed in front of the patient's eye. The handheld lens produces an image that is visualized through the oculars of the biomicroscope. Unfortunately, this technique suffers from significant image aberrations induced by light reflections off the handheld lens, which limits the practical view to only a thin slice of retina comprising less than 1% of the total retina surface area. FIG. 1B is a typical image of the retina provided by slit beam illumination and a handheld lens. Note the limited field of view and significant lens reflections present. The position of the slit must be maneuvered to examine different parts of the retina. Image quality even from this slit is often significantly degraded, making retinal diagnosis difficult. In contrast, conventional retinal photography routinely is capable of 50 degree aberration and reflection free fields of view of the retina. FIG. 1C is a standard fundus camera image of a retina. There is significantly greater retinal detail and a much wider field of view compared to the slit lamp image of FIG. 1B. No lens reflections or image aberrations are present, greatly facilitating diagnosis of retinal diseases. Unfortunately, these photographic advances have yet to be translated in any meaningful way into improvements in the clinical exam.
There are currently 16 million diabetic patients in the United States who require yearly, dilated retina exams as part of their recommended eye care. Half of these patients will have some form of retinopathy present at the time of exam. For the majority of these patients, slit lamp retinal examination is the only modality used to document their retinal findings. Retina photos are used as an adjunct to the clinical exam in only 10-20% of patients, as this involves separate time consuming procedures by the ophthalmic photographer. This makes it imperative that a clear and reliable view of the retina is available to the clinician for accurate diagnosis.
Ten percent of diabetic patients will eventually develop proliferative diabetic retinopathy, requiring panretinal laser photocoagulation (PRP) to ablate their peripheral retina in an attempt to preserve central foveal vision. FIG. 2A illustrates a retina after PRP. Laser photocoagulation may be delivered via slit lamp techniques using widefield (>75 degree field of view) handheld lenses. These lenses, relying on the same slit illumination, suffer significantly greater reflection artifacts than the narrow field (<75 degree field of view) handheld lenses used for clinical exam of the macula. FIG. 2B illustrates a clinician's view at a slit lamp while performing PRP. A handheld contact lens is applied to a patient's eye and slit lamp illumination is used to visualize the retina and the aiming beam for the laser. Retinal detail is severely compromised from lens reflections and the limited field of view afforded by the slit illumination. The risk of inadvertent laser to the fovea is significant due to the obscuration of the optic nerve by this pattern of poor illumination and lens reflections. The slit beam must be constantly moved to reorient to the location of the optic nerve to verify retinal position and avoid inadvertent ablation of the central vision with laser. The limited and generally poor illumination provided by the slit beam substantially increases the time required for laser treatment and poses a significant and unnecessary safety hazard due to poor identification of retinal location.
Many diabetic patients with proliferative diabetic retinopathy proceed to develop chronic vitreous hemorrhages and decreased vision, requiring surgical removal of the blood in some cases. Poor illumination also poses a safety hazard for their retinal surgery. Standard pars plana vitrectomy technique relies on fiber optic illumination provided by a rigid 20 or 23 gauge probe inserted through the pars plana of the eye. Limited beam divergence of the fiber optic probe provides spot illumination of the retina, with details of the surrounding peripheral retina remaining poorly illuminated, as seen in FIG. 2C. This leads to an increased likelihood of instrument error causing permanent retinal damage. Greater surgical safety and decreased surgical times would be facilitated by a widefield general illumination of the retina in addition to the spot illumination provided by the fiber optic probe.
Commercial developments in ophthalmic photography over the last 40 years have clearly demonstrated that the retina can be imaged at high resolution and that image distortions/reflections can be fully corrected to enable accurate diagnosis of retinal disease. The hallmark of the difference in retinal photography over clinical exams is the different pattern of illumination used in each, as illustrated in FIG. 3A. Contemporary retina cameras generate a ring or “donut” of illumination centered on the pupil. This circular illumination provides an even/full illumination of the retina with minimal lens reflections. Imaging rays reflected from the back of the retina are collected from the middle of the “donut,” which substantially decreases lens reflections. Most commercial retina cameras are able to obtain a 50 degree field of view of the retina with this technique FIG. 1C, but are not able to achieve widefield (>75 degrees field of view) images such as shown in FIG. 2A.
Narrowfield cameras are non-contact, with the camera never touching the front surface of the eye. In contrast, widefield cameras often require direct contact of the imaging system with the cornea. The commercial RETCAM II retinal camera is an example of a widefield camera which directly contacts the cornea. This camera creates a donut of light using a solid fiber optic ring to couple an external illumination light directly to the cornea, as shown in FIG. 3E. FIG. 3C shows a sample image from the Retcam II. This illumination design, while a significant improvement on slit lamp illumination, still suffers from significant corneal haze, as well as unevenness in central illumination, as compared to peripheral illumination, due to issues with the illumination design. Further, the RETCAM II is designed for retinal photography and as specified is not capable of use in handheld clinical examination through a slit lamp biomicroscope. The device has electrical power and fiber optic light coupled into a sizable imaging wand that is significantly larger than existing handheld fundus lenses, severely limiting the unit's portability and ease of use. The design of the illuminating ring requires intricate manufacturing that would not be amenable to inexpensive handheld lenses. All these issues are addressed in various embodiments of the present invention, which is a significant improvement over contemporary designs.
An improved method of illumination is needed to provide a wider field of view of the retina and to eliminate those lens reflections that result from external slit illumination of the handheld condensing lens. The ideal illumination for the retina is a ring of light focused on the eye with a diameter slightly less than the pupil diameter. Prior designs (Pomerantzeff et al., U.S. Pat. No. 3,944,341, and Massie et al., U.S. Pat. No. 5,822,036, of which are incorporated by reference herein in their entirety) have adapted a method of illumination into designs for retinal photography, as opposed to clinical examination. These two designs rely on an external illumination device that is then routed by means of fiber optic coupling into a contact lens that is used to view the retina.
These existing devices, while may be an improvement over non-illuminated handheld lenses, suffer from a number of design constraints that do not allow them to be used for handheld fundus examination at the ophthalmic slit lamp. Pomerantzeff relies on two rows of individual fiber optic elements that are cemented into a contact lens with the fiber optics directly contacting the cornea. This presents issues with sterilization due to the inevitable breakdown of the cementing compound and lodging of bacteria into the cemented area surrounding it. It also requires technically difficult fiber optic polishing so that the individual fibers do not damage the cornea and are all at the same plane. By focusing the ring of light on the cornea through means of fiber optics, significant corneal haze is generated which lowers overall image contrast. There is a complicated five stage optical element design to produce an image which leads to an unnecessarily bulky lens that could not be easily manufactured or handheld due to its overall size. The directionality of the fiber optics, while illuminating some of the peripheral retina, do not illuminate the central portion of the retina well, leaving the macula less exposed to light compared to the peripheral retina. A separate illuminator is required that is external to the device, requires electrical power, and limits portability of this device. The device is intended for retinal photography and is not optimized or usable for slit lamp examination. The focus of the five lens design is intended to focus reflected retina light on an imaging device directly attached to the lens, rather than at the distances required by ophthalmic slit lamp examination. Finally, the patent has not resulted in a commercial device in the years since it was originally issued.
The patent by Massie et al. has similar limitations to the earlier design of Pomerantzeff. Fiber optic illumination is used to direct the light from an external illumination source into the imaging lens, reducing portability of the unit. The device is intended only for retinal photography with an imaging device built into the handheld unit and then electrically connected to a larger external imaging control unit. There is no clear optical axis that would allow use of the device at the ophthalmic slit lamp. The design is intended to focus the light from the retina onto an imaging device that is located directly behind the contact lens rather than at the distances required by handheld condensing lenses used at an ophthalmic slit lamp. The use of fiber optics for coupling of an external illumination source limits the diffusion of the illuminating light beam and provides only partial illumination of the retina with a dark central retina, as also seen with the Pomerantzeff design. While the Massie design allows for illumination by placing a second central illumination source contained within the handheld unit itself to illuminate central retina, it obscures the central axis of the lens, which eliminates visualization of the retina through the center of the lens; a function essential to a handheld condensing lens. The design additionally attempts to improve the illumination produced by fiber optic through use of up to three additional lens elements at the end of the fiber optic, which again complicates construction and alignment of this device. Similar to the Pomerantzeff design, Massie's coupling of light fiber optically directly to the corneal surface results in significant corneal haze which degrades image contrast.
Fine polishing of the fiber optic is required to angle the exit of the light to improve the area of the retina illuminated. However, the angle cut required on the fiber optic reduces transmission of the light due to the oblique exit of the light from the fiber optic element. Finally, the design of the Massie device results in a bulky imaging unit that far exceeds the typical 40 mm depth of a handheld fundus lens. All of these design issues that are optimized for retinal photography limit the ability of this design to be used as a self illuminated handheld condensing lens for retinal examination.
Next, Miller et al., U.S. Pat. No. 7,048,379, discloses an imaging lens and illumination system for a retinal camera. Miller's ring illumination was focused on the patient's retina through a front objective lens. The lighting is located behind the objective lens, and the camera is not designed with a contact lens.
Contemporary retinal photography designs are capable of attaining better quality images and a wider field of view with less reflections than conventional slit lamp illumination. However, they remain limited by size, portability, poor illumination, and poor image contrast. Massie and Pomerantzeff produced devices which have no direct view through the lens that is available for the practitioner to directly visualize the retina (as both are intended for retinal photography) and are too large to be of practical use in clinical examination. Further, their complicated designs render them expensive to manufacture. Finally, they still suffer from problems with full and even illumination.
Providing the versatility and speed of clinical examination with the accuracy and clarity of retinal photography would provide greatly improved image quality, permitting significantly wider fields of view, better resolution of retinal detail for diagnosis, and safer surgical intervention to treat retinal disease.